To
remedy this evil, Mr. Newman is now engaged in obtaining porcelain troughs.
The other disadvantage is a precipitation of copper on the zinc plates. It
appears to me to depend mainly on the circumstance that the papers between
the coppers retain acid when the trough is emptied; and that this acid
slowly acting on the copper, forms a salt, which gradually mingles with the
next charge, and is reduced on the zinc plate by the local action (1120.):
the power of the whole battery is then reduced. I expect that by using
slips of glass or wood to separate the coppers at their edges, their
contact can be sufficiently prevented, and the space between them be left
so open that the acid of a charge can be poured and washed out, and so be
removed from _every part_ of the trough when the experiments in which the
latter is used are completed.

1134. The actual superiority of the troughs which I have constructed on
this plan, I believe to depend, first and principally, on the closer
approximation of the zinc and copper surfaces;--in my troughs they are only
one-tenth of an inch apart (1148.);--and, next, on the superior quality of
the rolled zinc above the cast zinc used in the construction of the
ordinary pile. It cannot be that insulation between the contiguous coppers
is a disadvantage, but I do not find that it is any advantage; for when,
with both the forty pairs of three-inch plates and the twenty pairs of
four-inch plates, I used papers well-soaked in wax[A], these being so large
that when folded at the edges they wrapped over each other, so as to make
cells as insulating as those of the porcelain troughs, still no sensible
advantage in the chemical action was obtained.

[A] A single paper thus prepared could insulate the electricity of a
trough of forty pairs of plates.

1135. As, upon principle, there must be a discharge of part of the
electricity from the edges of the zinc and copper plates at the sides of
the trough, I should prefer, and intend having, troughs constructed with a
plate or plates of crown glass at the sides of the trough: the bottom will
need none, though to glaze that and the ends would be no disadvantage. The
plates need not be fastened in, but only set in their places; nor need they
be in large single pieces.

S 17. _Some practical results respecting the construction and use of the
Voltaic Battery_ (1034. &c.).

1136. The electro-chemical philosopher is well acquainted with some
practical r